linux-kernel - Re: [PATCH v2 2/4] Documentation: Add documentation for APM X-Gene SoC PMU DTS binding

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Date:	Mon, 2 May 2016 15:56:48 -0500
From:	Rob Herring <robh@...nel.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Tai Tri Nguyen <ttnguyen@....com>,
	Mark Rutland <mark.rutland@....com>, catalin.marinas@....com,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	patches <patches@....com>
Subject: Re: [PATCH v2 2/4] Documentation: Add documentation for APM X-Gene
 SoC PMU DTS binding

On Wed, Apr 20, 2016 at 12:31:22PM +0100, Will Deacon wrote:
> On Mon, Apr 18, 2016 at 01:04:53PM -0700, Tai Tri Nguyen wrote:
> > >> +Required properties for MCB subnode:
> > >> +- compatible         : Shall be "apm,xgene-pmu-mcb".
> > >> +- reg                        : First resource shall be the MCB PMU resource.
> > >> +- index                      : Instance number of the MCB PMU.
> > >> +
> > >> +Required properties for MC subnode:
> > >> +- compatible         : Shall be "apm,xgene-pmu-mc".
> > >> +- reg                        : First resource shall be the MC PMU resource.
> > >> +- index                      : Instance number of the MC PMU.
> > >
> > > Don't use indexes. You probably need phandles to the nodes these are
> > > related to.
> > >
> > > How many variations of child nodes do you expect to have? 2, 10, 50? You
> > > might want to just collapse all this down to a single node and put this
> > > information in the driver if it is fixed for each SoC and there's only a
> > > handful.
> > >
> > 
> > For each kind of PMU, for example memory controller PMU, I expect to
> > have the number of instances up to 8.
> > They are actually all independent PMU nodes and have their own CSR memory bases.
> > The indexes are used for exposing the devices to perf user only. It
> > doesn't have an impact on the programming model.
> > Mark also had the same concern.
> 
> Regardless, I'll need an ack from Rob or Mark before I can merge this.

I still have a concern with this. Needing an index to expose to the user 
is generally not a valid reason. That's OS specific and therefore 
doesn't belong in DT.

Rob